Process for the manufacture of magnesium products



Ncv.119,11)35. w H. ifAR'NswoFeTl-ly Er AL 2,021,501`

' PROCESS FOR THE MANU'ACTURE 4O1 MAGNESIUM PRODUCTS Original Filed April, 29,' 1932 ATTOPNEV water is-indic'ated at Il. From Il the ,slum hydroxide.

Patented Nov. 19, 1.935

rnocEs's Fon THE MANUFAGTURE F MAGNESIUM rnonuc'rs william n. Farnsworth, Manatee, Mien., :ma

Montel Montgomery,

Los Angeles, Calif., as-

signors to Marine Chemicals Company, Ltd.,

South San Francisco, Delaware Calif., a corporation of continuation er apuestan serial No. 608,202, April 29, 1932. This application May 21, 1934,

l serial No. 726,032

3 Claims. (Cl. 23-201) 'lhis invention .relates generally to processes for the manufacture of magnesium products, such as magnesium hydroxide or magnesium carbonate, from brines containing convertible magnesium salts, salts .as magnesium chloride,v magnesium sulphate, magnesium bromide, and the like.

' The process disclosed herein is applicable to relatively dilute brine, such as sea water, sea water concentrates, or to more concentrated inland brines.

It is an object of the invention to provide a process of the above character which will make possible the manufacture of the desired magnesium products at a minimum cost. To this end our process is characterized by the precipitation of magnesium hydroxide from the brine, in such physical'form that subsequent concentration and washing of the precipitated magnesium hydroxide are greatly facilitated. f

A further object of the invention is to provide a processor the above character which is readily controllable, and which will facilitate production of magnesium products of uniform quality.

Further objects of the invention will /appear from the following description in which the preferred embodiments of the invention have been set forth/,in detail in conjunction with the accompanying drawing.l 'I'he appended claims are to be accorded a range of equivalents consistent with ,the state of the prior art.

v In the past, it has been proposed to react brine containing convertible magnesium salts, with calcium'hydroxide in solution, to precipitate magne- In such processes the magnesium hydroxide precipitated 4is in amorphous or gelatinous form. It is diicultto effect a separation between such amorphous magnesium hydroxide vand the brine from which it is preciplitated, for the reason that its settling rate is less than .3 foot per hour and is often as low as about l inch per 24hours. We have found that a reaction with calcium hydroxide particles carried out in the absence of material amounts of calcium hydroxide in free solution, results in the precipitation of magnesium hydroxide having a relatively high. settling rate.

Our process can be explained in detail by 'reference to the accompanying drawing, which is a flow sheet of a specinc embodiment of our process. as applied to sea 'waterf Storage f sca g water is caused to flow through the mixing tank II and then through the pre-treatment retention tanks I2 and I3. Calcium hydrate, preferably in the form or a highly reactive elw?, 1B @reduced at II and a reaction between the lime and the sea water occurs in tanks I2 and I3. This pretreat- 1nent is carried out primarily for the purpose of removing calcium bicarbonate usually present insea water, and to precipitate simultaneously oth- 5 er removable impurities such as suspended solid matter, silica and the like, rather than to precipitate magnesium hydroxide in substantial quantities; therefore a minimum amount of lime is employedyto accomplish the desired resuits. J

' It may be explained at this point that sea water contains many salts, including calcium bicarbonate; magnesium chloride, magnesiumv sulphate, and magnesium bromide. Since these salts are precipitated by treatment of the sea water with lime, it is desirable that the calcium bicarbonate' is removed by a preliminary treatment, in order to prevent`contaminat/ion ofthe desired magnesium productsby salts insoluble in the mother liquor, such as calcium carbonate. Because of the presence of magnesium chloride and magnesium sulphate, it has been found necessary` to introduce substantially twice the amount of lime theoretically required to remove the calcium bicarbonate. In other words, to precipitate one gram of calciumybicarbonate the addition of 0.915 `gram of calcium hydrate is required. 'The calcium bicarbonate is precipitated in the form of calcium`carbonate, and a slight amount of magnesium hydroxide is also precipitated. l

From the tank I3 the pretreated brine is passed through a suitable filter I4, to remove the precipitate resulting from the pretreatment, and

to also remove any remaining silt or other foreign material. The flow of brine from filter Il is split; theI major portion, say 95%, is introduced directly into a reaction tank I8, while the re mainder is diverted through armixing vessel I'I. 4 Lime hydrate, in finely divided condition, is introduced into` vessel`l'l and thoroughly intermingled with the brine. From vessel I1, the brine, together with the calciumv hydrate which has been introduced into` the same, flows into a reaction tank I8, where it is mixed withthe remainingportion of the sea water, the outflow of whichis introduced into the setting tank IG.

The-calcium hydrate introduced at I1 shouldhave relatively high, availability, and is preferably suihciently finely divided to pass through a 60- mesh screen.

As the diverted portion of the brine is-contacted with the dry calcium hydrate, a reaction immediately commences between the calcium The precipitated magnesium hydroxide forms as a nlm about each lime particle. Such a nlm does not prevent further reaction, as it is 4permeable to the surrounding brine, but it does retard the speed of the reaction. As thereaction progresses in vtank i8, particles of magnesium hydroxide are formed .which rapidly settle out by gravity. The settling rate is in excess oi .3 foot per hour, and in actual practice has exceeded 1 foot per hour.

Microscopic studies of the magnesium hydroxide particles precipitated by our process have disclosed that the physical properties of the magnesium hydroxide diier from the amorphous or gelatinous form, there being distinct evidence of crystallization.

The precipitated magnesium hydroxide settles within tank i6, and can be removed as an underow concentrate. This concentrate can be washed by well-known counterflow methods, and can be further treated in any desired manner to form commercial products, such as milk of magnesia or magnesilun carbonate.

With dilute brines such as sea water, we have found it preferable to partially carry out the reaction between the calcium hydrate and the brine, prior to introducing the calcium hydrate into'the'settling tank i6. It the dry calcium hydrate is introduced directly into tank I6, there is a tendency for the lime particles coated with magnesium-hydroxide to settle before reaction with the brine is completed, resulting in limev contamination of the magnesium hydroxide concentrate.

While our process is applicable'to batch operations, it is preferably conducted continuously to secure utmost capacity for a given equipment. In

continuous operation, the ow of brine between the diiIerent parts otthe apparatus is continuous, magnesium hydroxide concentrate is continhydrate and the convertible magnesium salts, in which magnesium hydroxide is precipitated.

ually removed from the settling tank Il, and calcium hydrate is continuously introduced into vessel I'I.

The present application is a continuation o copending application Serial No. 608,202, ille 5 April 29, 1932. l

We claim:

1. In a. process ior manufacturing magnesium products from brine containing convertible magnesium salts, the steps of initially forming a mal0 terial consisting of calcium hydrate particles which have a lm coating of magnesium hydroxide, said material being formed apart from the main body of -the brine to be treated and containingsubstantially no lime in free solution, and then utilizing such material to react with the mainbody of the brine at a controlled rate.

2. In a process for manufacturing magnesium products from brine containing convertible magnesium salts, the steps of initially forming a material consisting of calcium hydrate particles which have a film coating of magnesium hydroxide, said material being formed apart from the main body of the brine to be treated and containing substantially no lime in free solution and substantially no magnesium hydroxide except s aid fllm coating, introducing said material to the, main body of the brine, and then permitting all' the precipitated magnesium hydroxide to settle through the mother liquor.

3. In a process for manufacturing magnesium products from brine containing convertible magnesium salts, the steps of premixing dry calvcium hydroxide with a minor portion of the brine, contacting the entire mix with the main body of the brine, and then permitting all of the precipitated magnesium hydroxide to settle through the mother liquor.

WILLIAM H. FARNSWORTH. 40 MONTEL MONTGOMERY. 

